Onboard fuel separation for octane-on-demand using membrane distillation

Abstract

The present application is directed to systems and methods for on-board fuel separation. The system includes: a source fuel tank for liquid fuel; a pump; and a membrane module. The membrane module includes a hydrophilic membrane, a retentate channel, and a permeate channel. The retentate and permeate channels are on opposing sides of the membrane. The membrane module receives fuel from the source fuel tank and separates the liquid fuel into a high octane fraction that collects in the retentate channel and a low octane fraction that diffuses through the membrane to the permeate channel. The system further includes a low octane fuel tank for receiving at least a portion of the low octane fraction, a high octane fuel tank for receiving at least a portion of the high octane fraction, and an engine configured to selectively receive at least a portion of the low and high octane fractions.

What is claimed is: 
     
       1. A system for on-board fuel separation using membrane distillation, the system being mounted in a vehicle, comprising:
 a source fuel tank comprising liquid fuel; 
 a pump configured to deliver the liquid fuel from the source fuel tank; 
 a membrane module comprising a hydrophilic membrane, a retentate channel, and a permeate channel, the retentate and permeate channels being disposed on opposing sides of the hydrophilic membrane, wherein the retentate channel and the permeate channel are configured to receive the liquid fuel from the source fuel tank via a feed channel, and wherein the membrane module is configured to separate the liquid fuel via membrane distillation in which temperature and partial pressure differences between the retentate and permeate channels create a chemical potential difference between the retentate channel and permeate channel such that a high octane fraction remains in the retentate channel and a low octane fraction diffuses through the hydrophilic membrane to the permeate channel; 
 a low octane fuel tank configured to receive the low octane fraction from the permeate channel; and 
 a high octane fuel tank configured to receive the high octane fraction from the retentate channel, wherein an engine is fluidly connected to the permeate channel and the retentate channel, and configured to selectively receive at least a portion of the low octane fraction and at least a portion of the high octane fraction. 
 
     
     
       2. The system of  claim 1 , further comprising:
 a preheater configured to preheat the liquid fuel prior to delivery of the liquid fuel to the retentate and permeate channels of the membrane module. 
 
     
     
       3. The system of  claim 1 , wherein the hydrophilic membrane is in the form of a flat sheet, a hollow fiber, or a spiral wound. 
     
     
       4. The system of  claim 1 , further comprising:
 a heat exchanger fluidly connected to the retentate channel and configured to maintain a temperature of the retentate channel to enhance separation of the high octane fraction from the low octane fraction in the membrane module. 
 
     
     
       5. The system of  claim 1 , wherein the liquid fuel is gasoline, naphtha, or diesel fuel. 
     
     
       6. A system for on-board fuel separation using membrane distillation, the system being mounted in a vehicle and comprising:
 a source fuel tank comprising liquid fuel; 
 a pump configured to deliver the liquid fuel from the source fuel tank; 
 a membrane module comprising a hydrophilic membrane, a retentate channel, and a permeate channel, the retentate and permeate channels being disposed on opposing sides of the hydrophilic membrane, wherein the retentate channel is configured to receive the liquid fuel from the source fuel tank via a feed channel, wherein the feed channel is further configured to receive a solvent for enhancing the separation of a low octane fraction and a high octane fraction, and wherein the membrane module is configured to separate the liquid fuel via membrane distillation in which temperature and partial pressure differences between the retentate and permeate channels create a chemical potential difference between the retentate channel and permeate channel such that the high octane fraction remains in the retentate channel and the low octane fraction diffuses through the hydrophilic membrane to the permeate channel; 
 a gas channel fluidly connected to the permeate channel and configured to deliver a sweeping gas to the permeate channel; 
 a first flash tank fluidly connected to the permeate channel and configured to selectively receive at least a portion of the low octane fraction and the sweeping gas, and to separate the low octane fraction from the sweeping gas; 
 a low octane fuel tank configured to receive the separated low octane fraction from the first flash tank; 
 a second flash tank configured to receive the high octane fraction and the solvent from the retentate channel and separate the high octane fraction from the solvent; and 
 a high octane fuel tank configured to receive the high octane fraction from the second flash tank, wherein an engine is fluidly connected to the permeate channel and configured to selectively receive at least a portion of the low octane fraction and at least a portion of the high octane fraction. 
 
     
     
       7. The system of  claim 6 , further comprising:
 a preheater configured to preheat the liquid fuel prior to delivery of the liquid fuel to the retentate channel of the membrane module. 
 
     
     
       8. The system of  claim 6 , further comprising:
 a condenser fluidly connected to the permeate channel and the feed channel, and configured to condense the low octane fraction prior to delivery of the low octane fraction to the engine or the low octane fuel tank. 
 
     
     
       9. The system of  claim 6 , wherein the hydrophilic membrane is in the form of a flat sheet, a hollow fiber, or a spiral wound. 
     
     
       10. The system of  claim 6 , further comprising:
 a heat exchanger fluidly connected to the retentate channel and configured to maintain the temperature of the retentate channel to enhance separation of the high octane fraction from the low octane fraction in the membrane module. 
 
     
     
       11. The system of  claim 6 , wherein the liquid fuel is gasoline, naphtha, or diesel fuel. 
     
     
       12. A method for on-board fuel separation in a vehicle using membrane distillation, the method comprising:
 pumping liquid fuel from a source fuel tank to a membrane module, wherein the membrane module comprises a hydrophilic membrane, a retentate channel, and a permeate channel, the retentate and permeate channels being disposed on opposing sides of the hydrophilic membrane; 
 supplying a solvent to the liquid fuel upstream of the membrane module before pumping the liquid fuel into the membrane module; 
 separating, via the membrane module, the liquid fuel into a high octane fraction and a low octane fraction via membrane distillation in which temperature and partial pressure differences between the retentate and permeate channels create a chemical potential difference between the retentate channel and permeate channel, wherein the high octane fraction collects in the retentate channel and the low octane fraction diffuses through the hydrophilic membrane to the permeate channel, and wherein the solvent enhances the separation of the low octane and high octane fractions in the membrane module; 
 separating the high octane fraction from the solvent via flash distillation in a flash tank; 
 selectively delivering at least a portion of the high octane fraction from the flash tank to a high octane fuel tank or to an engine of the vehicle; and 
 selectively delivering at least a portion of the low octane fraction from the permeate channel to a low octane fuel tank or to the engine of the vehicle. 
 
     
     
       13. The method of  claim 12 , further comprising:
 preheating the liquid fuel prior to its delivery to the membrane module. 
 
     
     
       14. The method of  claim 12 , further comprising:
 heating the retentate channel via a heat exchanger to enhance separation of the high octane fraction from the low octane fraction. 
 
     
     
       15. The method of  claim 14 , wherein the heat exchanger produces heat using a hot coolant or an exhaust gas. 
     
     
       16. The method of  claim 12 , further comprising:
 passing a sweeping gas stream through the permeate channel to produce a mixture of sweeping gas and the low octane fraction; 
 condensing the low octane fraction in a condenser prior to delivery of the low octane fraction to the engine or the low octane fuel tank; and 
 separating the low octane fraction from the sweeping gas via another flash tank prior to delivery of the low octane fraction to the low octane fuel tank. 
 
     
     
       17. The method of  claim 12 , wherein the hydrophilic membrane is in the form of a flat sheet, a hollow fiber, or a spiral wound. 
     
     
       18. The method of  claim 12 , wherein the liquid fuel is gasoline, naphtha, or diesel fuel.